a. Field of Use
Many power sources, and particularly internal combustion engines, have speed-torque curves which do not match the speed-load curve of the driven equipment well, and, in any event, the speed-load curve of a given piece of equipment can, and often does, vary widely with operating conditions. A prime example of this situation is the internal combustion engine powered automobile, although it also occurs in many other cases.
Two general solutions to the problem of obtaining a tolerable match between power plant performance characteristics and operating load requirements have become widely adopted from among many proposed solutions. The first of these is a clutch and manually operated gearbox offering a choice of two or more gear ratios appropriate for use at different speeds and loads. Disadvantages of such transmissions include the level of skill and coordination required to operate them, the limited number of well matched steps available, and the severe wear involved in changing from one gear to another.
The other general solution which has been widely adopted is that of the so-called "automatic" transmission involving a fluid filled turbine clutch drive, usually with "torque converter" features to reduce slippage at start-up, coupled to a multiple ratio gearbox provided with speed-torque responsive equipment for automatically shifting from one gear ratio to another at appropriate times. (Such gearboxes often include planetary gear trains). Disadvantages of such transmissions include the complexity and consequent expense of the equipment, liability to leakage in the hydraulic portion of the system, and the necessity for sensitive adjustments in the shifting control apparatus.
In accordance with the present invention, a simple all gear-and-shaft automatic transmission is provided in which the speed-torque characteristics of the power source are automatically and efficiently matched to the speed-torque requirements of the load. The transmission of the invention may replace conventional transmissions in automotive and other applications where speed-torque matching between power source and load is inherently poor over significant operating ranges.
B. Certain Prior Art
Planetary gear transmissions fall into two broad classes. In both, the planetary gears are arranged to mesh with, and revolve about, a central sun gear, and are carried in their revolution on a rotatable plate or similar structure called a carrier or cage. In one type, the planetary gears are bounded by an internally toothed ring gear, while in the other type they are not. It should be noted that in the second type, it is known that the torque transmission through the gear train is a function of the rate of rotation of the rotatable cage.
Prior workers have proposed to exploit this knowledge in various ways to produce automatic transmissions and speed-change devices. Some use a cone pulley driven by the power source to drive the cage at varying speeds. See U.S. Pat. Nos. 729,601; 2,164,818. Others selectively engage the cage to the prime mover through various forms of clutches to control cage rotation. See U.S. Pat. Nos. 1,299,629; 1,804,037; 2,504,306; 2,884,812. Still others employ brakes of various sorts for controlling the speed of cage rotation. See U.S. Pat. Nos. 918,632; 1,153,261; 1,869,543; 2,409,551;, 2806,389; 2,901,925; 2,941,421; 3,448,828. A variety of other employments of planetary gear transmission systems have been suggested. See U.S. Pat. Nos. 1,765,948; 2,455,407; 2,459,969; 2,705,429; 2,794,350; 3,442,157; 3,481,221; 3,501,980; 3,511,113; 3,675,509; 3,842,685.